Appealing to Western individualism and a mistrust of federal government, activists have lined up some prominent conservatives, from one-time presidential hopefuls Tom Tancredo and Ron Paul to Republican-turned-Libertarian presidential candidate and former New Mexico Gov. Gary Johnson.

"This is truly a nonpartisan issue," said Mark Slaugh, a volunteer for the Colorado initiative who is based in Colorado Springs, which has more Republicans than anywhere else in the state.

"States' rights! States' rights!" Slaugh cried as he handed out flyers about the state's pot measure outside a rally last month by Republican vice presidential candidate Paul Ryan. Quite a few passing Republicans took the flyer.